Barbara Henning, the wife of British hostage Alan Henning, has urged his Islamic State captors to "please release him, we need him back home".
The 47-year-old aid worker was captured by militants in Syria last year and has been threatened with death by his Islamic State captors.
Iran is willing to work with the US to help defeat Islamic State (IS) militants, a senior Iranian government source has told Reuters.
However, Tehran would like to see more flexibility over its nuclear programme in exchange for helping Western powers tackle IS.
"Iran is a very influential country in the region and can help in the fight against the ISIL (IS) terrorists ... but it is a two-way street. You give something, you take something," the source was quoted as saying.
However, a Western diplomatic source said the countries negotiating over Tehran's nuclear programme were "determined not to bring the other subjects to the nuclear negotiations table".
The oldest member of Alan Henning's family has demanded boots on the ground to combat Islamic State militants who killed their beloved Alan.
The wife of a British aid worker held by Islamic State militants has recorded a message to his captors appealing for his life to be spared.